In cellular communications systems, physical (PHY) layer synchronization and Media Access Control (MAC) layer synchronization are performed before a mobile station can access a base station. For PHY layer synchronization, timing, frequency and power adjustment are made via Synchronization Channel (SCH) monitoring and tracking during downlink synchronization and via ranging operation during uplink synchronization. For MAC layer synchronization, system information acquisition, capability negotiation and registration are accomplished via network entry procedures. In IEEE 802.16m, three different types of ranging channels are defined. Under a non-synchronized ranging channel, the mobile station adjusts its frequency, timing, and power with its potential serving cell during initial network entry via initial ranging procedure, and adjusts its frequency, timing, and power with its target cell via handover procedure. Under a synchronized raging channel, the mobile station adjusts its frequency, timing, and power with its serving cell via period ranging procedure. Under a bandwidth request (BR) ranging channel, the mobile station sends out transmission intention and requirements during BR ranging procedure.
In order to meet different synchronization and performance requirements, the design and PHY structure of synchronized and non-synchronized ranging channels are different. In general, longer Ranging Cyclic Prefix (RCP) length is required for non-synchronized ranging channels due to longer propagation delay in cell-edge. In addition, subcarrier spacing is modified in non-synchronized ranging channels. FIG. 1 (Prior Art) illustrates a 3-symbol synchronous ranging channel defined in IEEE 802.16e. In FIG. 1, the 3-symbol synchronous ranging channel has a relative short RCP length, and three ranging code sequences are located in three OFDM symbols. FIG. 2 (Prior Art) illustrates two different formats of a non-synchronous ranging channel defined in IEEE 802.16m. In FIG. 2, TRCP is the RCP time length of a ranging channel, and TRP is the time length of the ranging channel signal waveform. As illustrated in FIGS. 1 and 2, the TRCP of a non-synchronous ranging channel is longer than the TRCP of a synchronous ranging channel.
Femtocell is anticipated to be an important feature to support extreme high-speed transmission for next generation 4G systems, especially in indoor environments. In femtocell environment, the network coverage is usually less than 30 meters. In addition, a femtocell stays in low-duty mode for most of the time, and normally serves no more than 10 users. While separate design for synchronous ranging and non-synchronous ranging channels may be desirable for macrocells, such separate design may not be desirable for femtocells because of the unique environment of femtocell. It remains a challenge to reduce femtocell complexity, improve spectrum efficiency, and reduce initial network entry latency in femtocell environment, while continue to satisfy various synchronization and performance requirement.